Japan's biggest organised crime syndicate has launched its own website, complete with a corporate song and a strong anti-drugs message, as the yakuza looks to turn around its outdated image and falling membership.

The clunky-sounding "Banish Drugs and Purify the Nation League" website is an offering from the Yamaguchi-gumi, Japan's largest yakuza grouping.

It includes shakily-shot footage of members making their New Year pilgrimage to a shrine. The soundtrack is a traditional folk-style song with lyrics extolling the virtues of the "Ninkyo" spirit -- an ideal of masculinity that battles injustice and helps the weak.

"Nothing but Ninkyo, that is the man's way of life," say the lyrics. "The way of duty and compassion, bearing the ordeal for our dream."

Another video shows men with crew cuts pounding sticky rice for a New Year festival, and there are galleries of pictures showcasing the clean-up work members did in the aftermath of the 2011 tsunami and the 1996 Kobe earthquake.

The website is not the Yamaguchi-gumi's first foray into media -- the crime syndicate last year began publishing a magazine for its members that includes a poetry page, senior gangsters' fishing diaries and a message from the boss.

Like the Italian mob or Chinese triads, yakuza syndicates are involved in activities ranging from prostitution to extortion and white-collar crime.

But unlike their underworld counterparts elsewhere, the yakuza are not illegal and each of the designated groups, like the Yamaguchi-gumi, have their own headquarters, with senior members dishing out business cards.

They have historically been tolerated by the authorities, sometimes with corrupt police overlooking their violence, and are routinely glamorised in fanzines and manga comics.

- membership at an all-time low -

But periodic crackdowns have gained momentum and there is evidence the mob's appeal is waning.

The number of people belonging to yakuza groups fell to an all-time low in 2013, slipping below the 60,000-member mark for the first time on record, police said last month.

An increasingly poor public image and Japan's flaccid economy have made the lives of the gangsters difficult, which has made membership less attractive for potential recruits, experts said.

The website, which looks outdated, is an attempt to counter the yakuza's image as "anti-social forces" -- the police euphemism for them -- by showing how neighbourly its members are, experts say.

One page shows men collecting litter along the banks of the Toga River near the Yamaguchi-gumi's headquarters in Kobe, western Japan, with a nearby sign reading: "Purge yakuza."

Jake Adelstein, a journalist and author who has written extensively on organised crime in Japan, said the Yamaguchi-gumi's online offering was an effort to prove its humanitarian credentials.

"By presenting an anti-drugs theme, it shows concern for social welfare, it shows pictures of the group doing emergency relief after the (2011) and Kobe earthquakes," he told AFP.

He said it was true that the yakuza made use of their "ties to the trucking industry and their abundance of cash, lack of red tape and institutional memory" to provide help after the disasters.

But, he added, "there was a certain amount of self-interest involved -- getting in with the locals helps them get a share of the reconstruction money."

Adelstein, whose account of his life working the crime beat for a Japanese newspaper is being made into a film starring Harry Potter actor Daniel Radcliffe, said the site was an attempt to whitewash an unsavoury truth.

"The yakuza motto is 'help the weak and fight the strong.' In practice, it's usually the reverse," he said.

Police officials said they could not immediately confirm the website was made by the Yamaguchi-gumi, nor comment on it.

The website, which comes complete with a "contact us" button, can be found at: http://zenkokumayakubokumetsudoumei.com/index.html